The comet assay, sometimes referred to as single cell gel electrophoresis (SCGE), is commonly used to measure the presence and extent of DNA damage induced by acute or chronic exposure to chemicals and/or radiation. It has gained popularity as a standard technique for the evaluating DNA damage and repair, biomonitoring, and genotoxicity testing.
A conventional comet assay involves, in sequence, encapsulating cells in a low-melting-point agarose suspension, lysing the cells in neutral or alkaline conditions to break down the cell membranes and expose the nucleoid, conducting electrophoresis of the nucleoids, and staining the nucleoids to visually and quantitatively determine the extent of DNA damage. The resulting electrophoresis patterns often resemble the shape of a comet, hence the name given to this technique.
The comet assay, similar to other cell separation and extraction techniques, requires a clean, level working surface that serves to chill the sample slides that are covered by the agarose gel encapsulating the cells to be examined. Because the agarose gel is typically cured (i.e., solidified) at a low temperature (approximately 4° C.), a chilling plate is required.
Currently available comet assay apparatuses utilize one of two mechanisms for cooling. The first mechanism involves cooling using ice that is housed in a container, the container being situated beneath a thermally conductive tray upon which the sample slides, with agarose gel, are placed. The second mechanism is by electrical cooling as described by Samson et al. (U.S. Pat. No. 9,128,046 B2).
Neither of these cooling techniques is ideal. In the case of cooling by ice, periodically filling the container with fresh ice is necessary to maintain a steady cooling temperature, uneven thawing of the ice upsets the balance of the thermally conductive tray, and formation of condensation are examples of unwanted side effects. On the other hand, an electrical cooling system typically requires additional energy input. Also, apparatuses operating on these two mechanisms require a considerable amount of space for equipment setup and can only accommodate a limited number of slides.
As a result, there still remains a need for a more convenient, space-saving, and easy-to-maintain system for handling and processing cell samples for comet assays, and other applications, where cooling and/or freezing is required.